Control device for internal combustion engine and control method for internal combustion engine

ABSTRACT

The control device includes an operation state detector, an intake manifold pressure detector, an air humidity detector, an air temperature detector, an atmospheric pressure detector, and a controller that controls the engine output on the basis of detection results of the detectors. The controller generates humidity information on the air which is taken in by the internal combustion engine, from the humidity, temperature, and atmospheric pressure, calculates a dry air partial pressure by correcting the pressure detected by the intake manifold pressure detector, by using the humidity information, and controls the engine output by taking the pressure detected by the intake manifold pressure detector as a wet air pressure and selecting, according to a control element, either one of the wet air pressure and the dry air partial pressure as a pressure to be used for the engine output control.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a control device for an internal combustionengine and a control method for an internal combustion engine thatcorrect an intake manifold pressure, which is used for calculatingcontrol parameter of the internal combustion engine, for humidity.

2. Description of the Related Art

An engine control method called “torque-based control” in which anengine output shaft torque is used as a value of drive power demanded bya driver or a vehicle and the torque generated by the engine iscontrolled by taking this engine output shaft torque as an indicator hasbecome popular in recent years.

In the torque-based control, the target torque of the engine isdetermined on the basis of the depression amount of the acceleratorpedal by the driver. The throttle opening degree is then controlled suchthat a target intake air flow rate enabling the generation of the targettorque is taken in by the engine. As a result, the engine output iscontrolled to the target torque by controlling the fuel injection amountor ignition timing according to the actual intake air flow rate, and thetravel performance demanded by the driver is realized.

The following technique has been suggested for an engine control devicethat controls the throttle opening degree by driving an actuator coupledto the engine throttle in order to realize the target intake air flowrate corresponding to such target torque of the engine. Thus, the targetopening area of the throttle is determined by using the target intakeair flow rate, the ratio of pressure before and after the throttle, andthe opening area of the throttle in a basic formula for flow ratecalculation in a restriction-type flowmeter. With this technique, theactuator coupled to the throttle is controlled such as to obtain thethrottle opening degree at which the target opening area of the throttleis attained.

In order to control, for example, the fuel injection amount and ignitiontiming, which are the engine control elements, it is necessary to detectthe amount of air taken into the engine. Two systems which are calledL-Jetronic and D-Jetronic are generally used for such detection.

In the L-Jetronic system, the amount of air which is taken in isdetected by an air flow sensor disposed in an intake channel. TheD-Jetronic system estimates the amount of air taken into a cylinder onthe basis of the intake manifold pressure downstream of the throttlevalve and the engine revolution speed.

The D-Jetronic system is inexpensive because no expensive air flowsensor is needed. Another advantage of the D-Jetronic system is that afast response to changes in the operation state is ensured by controlusing the pressure immediately before the cylinder.

A method for calculating the amount of air taken into a cylinder fromthe pressure and volume efficiency of the intake manifold and thecylinder volume and temperature is a specific example of methods forestimating the cylinder intake air amount in the D-Jetronic system (see,for example, Japanese Patent Application Publication (JP-A) No.H08-303293.

SUMMARY OF THE INVENTION

However, the following problems are associated with the related art. TheD-Jetronic system has the above-described merits, but the problemthereof is that the estimation is performed without directly measuringthe amount of air which is important in engine control and, therefore,an error occurs in the estimated amount of air.

In the environment in which engines are used, water vapors representedby humidity are typically contained in the air taken in by the engine.Furthermore, the amount of water vapors contained in the air, that is,the humidity varies depending on meteorological conditions and the like.Accordingly, the pressure in the intake manifold which is indicated inJP-A No. H08-303293 includes a pressure created by the water vaporscontained in the air, that is, a water vapor partial pressure.

In a gasoline engine, the output is adjusted by the amount of airsupplied to cylinders. This amount of air is adjusted by adjusting theopening degree of a throttle valve provided in the intake channel to thecylinder. A fuel such as gasoline is mixed with the air supplied to thecylinder, the gas mixture compressed by the piston is ignited, and theincrease in pressure generated by the combustion of the gas mixture isthe engine output.

Of the amount of air taken into the cylinder, only the dry air,excluding the water vapors contained in the air, takes part in thecombustion. The resultant problem is that even when the amount of wetair supplied to the cylinder is the same, the engine output differsdepending on the humidity of the wet air, that is, the amount of watervapor. In the D-Jetronic system, the water vapor partial pressure causesan error.

A method for reducing the intake air amount calculation error when anintake VVT or exhaust VVT is changed in the D-Jetronic system has beensuggested to resolve this problem (see, for example, Japanese Patent No.5328967). However, since the correction for the humidity is also notperformed in Japanese Patent No. 5328967, an error relating to thehumidity component is present at all times.

The present invention has been created to resolve the above-mentionedproblems, and it is an objective of the present invention to provide acontrol device for an internal combustion engine and a control methodfor an internal combustion engine that can accurately control the engineoutput without being affected by humidity, and can increase the accuracyof engine control, such as exhaust gas purification, while accuratelycontrolling the torque demanded by the driver.

The control device for an internal combustion engine in accordance withthe present invention includes: an operation state detector that detectsan operation state of an internal combustion engine; an intake manifoldpressure detector that detects a pressure in an intake manifolddownstream of a throttle valve provided in an intake channel of theinternal combustion engine; an air humidity detector that detects ahumidity of air taken in by the internal combustion engine; an airtemperature detector that detects the temperature of the air; anatmospheric pressure detector that detects an ambient pressure of theinternal combustion engine as an atmospheric pressure; and a controllerthat controls an engine output on the basis of detection results of thedetectors, wherein the controller: generates humidity information on theair which is taken in by the internal combustion engine, from thehumidity detected by the air humidity detector, the temperature detectedby the air temperature detector, and the atmospheric pressure detectedby the atmospheric pressure detector; calculates a dry air partialpressure by correcting the pressure detected by the intake manifoldpressure detector, by using the generated humidity information; andcontrols the engine output by taking the pressure detected by the intakemanifold pressure detector as a wet air pressure and selecting,according to a control element, either one of the wet air pressure andthe dry air partial pressure as a pressure to be used for controllingthe engine output.

The control method for an internal combustion engine in accordance withthe present invention is to be executed by a controller in a controldevice for an internal combustion engine, the control device including:an operation state detector that detects an operation state of aninternal combustion engine; an intake manifold pressure detector thatdetects a pressure in an intake manifold downstream of a throttle valveprovided in an intake channel of the internal combustion engine; an airhumidity detector that detects a humidity of air taken in by theinternal combustion engine; an air temperature detector that detects thetemperature of the air; an atmospheric pressure detector that detects anambient pressure of the internal combustion engine as an atmosphericpressure; and the controller that controls an engine output on the basisof detection results of the detectors, the control method including thefollowing steps executed by the controller: a first step for generatinghumidity information on the air which is taken in by the internalcombustion engine, from the humidity detected by the air humiditydetector, the temperature detected by the air temperature detector, andthe atmospheric pressure detected by the atmospheric pressure detector;a second step for calculating a dry air partial pressure by correctingthe pressure detected by the intake manifold pressure detector by usingthe humidity information generated in the first step; and a third stepfor controlling the engine output by taking the pressure detected by theintake manifold pressure detector as a wet air pressure and selecting,according to a control element, either one of the wet air pressure andthe dry air partial pressure as a pressure to be used for controllingthe engine output.

The present invention provides the configuration in which the intakemanifold pressure is taken as a wet air pressure, the pressure obtainedby correcting, by using the humidity information, the effect produced byhumidity on the intake manifold pressure is calculated as the dry airpartial pressure, and the pressure information to be used for thecontrol is switched, as appropriate, between the wet air pressure anddry air partial pressure according to the engine control element. As aresult, it is possible to provide a control device for an internalcombustion engine and a control method for an internal combustion enginethat can accurately control the engine output without being affected byhumidity, and can increase the accuracy of engine control, such asexhaust gas purification, while accurately controlling the torquedemanded by the driver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram illustrating schematically an internalcombustion engine control device according to Embodiment 1 of thepresent invention.

FIG. 2 is a block diagram illustrating the schematic configuration of anECU according to Embodiment 1 of the present invention.

FIG. 3 illustrates a torque curve in a certain operation state ofEmbodiment 1 of the present invention.

FIG. 4 illustrates a torque curve in a certain operation state, which isdifferent from that depicted in FIG. 3, and a knocking limit inEmbodiment 1 of the present invention.

FIG. 5 is a flowchart illustrating the processing sequence in thecontrol method for an internal combustion engine which is executed bythe ECU in Embodiment 1 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the control device for an internalcombustion engine and the control method for an internal combustionengine in accordance with the present invention will be explainedhereinbelow with reference to the drawings.

Embodiment 1

FIG. 1 is a configuration diagram illustrating schematically an internalcombustion engine control device according to Embodiment 1 of thepresent invention. In FIG. 1, an electronically controlled throttle 5that can be electrically controlled to adjust the intake air amount isprovided upstream of an intake system of an engine 1. A throttle openingdegree sensor 6 is provided for measuring the opening degree of theelectronically controlled throttle 5.

Provided also are an intake manifold pressure sensor 9 that measures apressure (referred to hereinbelow as “intake manifold pressure”) in aspace including the interiors of a surge tank 7 and an intake manifold 8(this space is referred to hereinbelow as “intake manifold”) downstreamof the throttle 5, and an intake manifold temperature sensor 18 thatmeasures the air temperature inside the intake manifold.

Provided outside the engine are an atmospheric pressure sensor 17 fordetecting the atmospheric pressure which is the ambient pressure of theengine, a temperature sensor 3 for detecting the ambient temperature,and a humidity sensor 4 for detecting the ambient humidity. Thosetemperature sensor 3 and humidity sensor 4 may be also provided at theengine intake channel or internal manifold.

A method may be also used by which the ambient pressure, ambienttemperature, and ambient humidity are obtained by communicatinginformation measured by other devices, such as an air conditioner. Whenthe temperature sensor 3 and the humidity sensor 4 are installed at theintake manifold, either one of the temperature sensor 3 and the intakemanifold temperature sensor 18 can be omitted to avoid measuring thetemperature in the same location.

The humidity sensor 4 is generally of an electric resistant type inwhich humidity is detected by the electric resistance of amoisture-sensitive material or an electrostatic capacitance type inwhich the humidity is detected by the electrostatic capacitance of asensor element. The humidity detected by the humidity sensor 4 is arelative humidity, regardless of the detection type thereof. Therelative humidity, as referred to herein, represents the ratio of thewater vapor partial pressure of the air to the saturated water vaporpressure determined by the air temperature, and even when the watervapor partial pressure in the air is the same, the relative humiditychanges depending on the temperature.

An injector 10 for fuel injection is provided in the vicinity of anintake valve including the interior of a cylinder and the intakemanifold 8. The intake valve and an exhaust valve are each provided withan intake VVT 11 and an exhaust VVT 12 for varying the valve timing. Anignition coil 13 for driving an ignition plug that generates a sparkinside a cylinder is provided at the cylinder head.

An air-fuel ratio sensor 15 and a catalyst (not depicted in the figure)are provided at the exhaust manifold 14. Only one of the intake VVT 11and the exhaust VVT 12 can be provided, and in some cases, none of themcan be provided.

Information on detection signals from a crank angle sensor 16 thatdetects a crank angle or engine revolution speed, the above-describedsensors, and other sensors which are not depicted in the figure, andinformation such as ignition S/W (referred to hereinbelow as “IG-S/W”)which is a start S/W of the engine are inputted as informationindicating the operation state of the engine 1 into an electroniccontrol unit (referred to hereinbelow as “ECU”) 20 constituted by amicrocomputer or an interface circuit.

The ECU 20, which corresponds to a controller, calculates a targettorque from the data indicating the inputted operation state andcalculates the target intake air flow rate at which the calculatedtarget torque is attained. The ECU 20 also calculates a target effectiveopening area and determines a target throttle opening degree by thebelow-described method so as to attain the target intake air flow rate.

The ECU 20 also controls the opening degree of the electronicallycontrolled throttle 5 such as to attain the target throttle openingdegree. At the same time, the ECU 20 calculates instruction values toactuators including the injector 10, the intake VVT 11, the exhaust VVT12, and the ignition coil 13.

The configuration of the ECU 20 of the engine control device accordingto Embodiment 1 will be described hereinbelow in greater detail withreference to FIG. 2. FIG. 2 is a block diagram illustrating theschematic configuration of an ECU 20 according to Embodiment 1 of thepresent invention.

The ambient temperature Thr detected by the temperature sensor 3, therelative humidity Hr of the ambient air which has been detected by thehumidity sensor 4, the atmospheric pressure Pa detected by theatmospheric pressure sensor 17, and the intake manifold pressure Pbdetected by the intake manifold pressure sensor 9 are inputted asinformation indicating the operation state to the ECU 20.

The ECU 20 is configured to include a saturated water vapor pressurecalculation unit 101, a water vapor partial pressure calculation unit102, a mole fraction calculation unit 103, a dry air partial pressurecalculation unit 104, a fuel injection amount calculation unit 105, anignition timing calculation unit 106, and a target throttle openingdegree calculation unit 107.

The saturated water vapor pressure calculation unit 101 inputs theambient temperature Thr and calculates a saturated water vapor pressurePs. The saturated water vapor pressure, as referred to herein, is apressure of water vapor when the water vapor is in a saturated state ata certain temperature. It is generally known that the saturated watervapor pressure can be calculated as a function of temperature by theTetens's formula represented by Expression (1) below. In Expression (1)below, T is a temperature (° C.); in the saturated water vapor pressurecalculation unit 101, the intake temperature Thr is indicated.

$\begin{matrix}{P_{S} = {6.1078\; \times {10^{(\frac{7.5 \times T}{T + 237.3})}\lbrack{hPa}\rbrack}}} & (1)\end{matrix}$

When the effect of index calculation on processing load causes concernin the calculation capacity of the ECU 20, the calculation may beperformed by table setting using the temperature, instead of calculatingby Expression (1) above.

The water vapor partial pressure calculation unit 102 inputs thesaturated water vapor pressure Ps and the relative humidity Hr andcalculates the water vapor partial pressure Pv. The water vapor partialpressure, as referred to herein, is a pressure created by water vaporcontained in the gas. The relationship thereof with the saturated watervapor pressure Ps is represented by Expression (2) below. In Expression(2) below, H is a relative humidity (% RH); in the water vapor partialpressure calculation unit 102, the relative humidity Hr is indicated.

$\begin{matrix}{P_{v} = {P_{S}\; \times {\frac{H}{100}\lbrack{hPa}\rbrack}}} & (2)\end{matrix}$

The mole fraction calculation unit 103 inputs the atmospheric pressurePa and water vapor partial pressure Pv and calculates the mole fractionχv. The mole fraction, as referred to herein, corresponds to humidityinformation indicating the ratio of the number of moles of water vaporand wet air, that is, the ratio of amounts of substances. The molefraction χv is the ratio of the amounts of substances of water vapor andwet air. Since the ratio of amounts of substances is equal to the ratioof pressures according to a generally known Dalton's law, the molefraction χv is represented by Expressions (3) to (5) below.

In Expressions (3) to (5) below, nv is the amount of the substance ofwater vapor, nd is the amount of the substance of wet air, Mv is themolecular weight of water vapor, Md is the molecular weight of dry air,mv is the mass of water vapor, and and is the mass of dry air.

$\begin{matrix}{n_{v} = \frac{m_{v}}{M_{v}}} & (3) \\{n_{w} = {{n_{v} + n_{d}} = {\frac{m_{v}}{M_{v}} + \frac{m_{d}}{M_{d}}}}} & (4) \\{X_{v} = {\frac{n_{v}}{n_{v} + n_{d}} = \frac{P_{v}}{P_{a}}}} & (5)\end{matrix}$

The dry air partial pressure calculation unit 104 inputs the intakemanifold pressure Pb, that is, the wet air pressure Pw, and the molefraction χv corresponding to the humidity information and calculates thedry air partial pressure Pd. The engine obtains the output by combustionof the mixed gas of air and gasoline inside the cylinders, but thiscombustion is caused by the dry air taken into the cylinders. Therefore,the amount of dry air is obtained by subtracting the water vaporfraction from the amount of air taken into the cylinders.

When the intake air amount is restricted in the throttle valve 5, thepressure downstream of the throttle valve becomes lower than the ambientatmospheric pressure, but the ratio of the amount of dry air and theamount of water vapor in the wet air which is taken in is the same asbefore passing the throttle valve. Therefore, the share of pressurecreated by the dry air in the intake manifold pressure is represented byExpression (6) below from the relationship represented by Expression (5)above. Here, Pd is the dry air partial pressure.

P _(d)=(1−χ_(v))×P _(w)  (6)

Fuel control or ignition control with the L-Jetronic system is generallyperformed by using a computational formula or a preset map on the basisof the amount of air detected with the air flow sensor and the enginefilling efficiency calculated from the amount of air and the enginerevolution speed.

Meanwhile, with the D-Jetronic system, fuel control or ignition controlis performed by calculations from the intake manifold pressure andengine revolution speed by using a preset map, or by a method similar tothat of the L-Jetronic system in which the intake air amount iscalculated, for example, from the computational formula indicated inJP-A No. H08-303293 by using the intake manifold pressure.

The fuel injection amount calculation unit 105 and the ignition timingcalculation unit 106 are explained below by considering a method inwhich control is performed using the intake air amount calculated fromthe intake manifold pressure. The intake air amount Qvth in this case iscalculated from the intake manifold pressure, for example, by Expression(7) below. Here, P is an intake manifold pressure, Kv is a volumeefficiency correction coefficient, Vcyl is a cylinder volume, Tsgt is aperiod between reference crank angles which is used for engine control,R is a gas constant, and Tb is an intake manifold temperature.

$\begin{matrix}{Q = \frac{P \times K_{v} \times V_{cyl}}{T_{sgt} \times R \times T_{b}}} & (7)\end{matrix}$

For example, the volume efficiency correction coefficient Kv iscalculated from the engine revolution speed and intake manifoldpressure. Thus, the results measured in advance are set as a map, andcorrection coefficients of volume efficiency are indicated for a varietyof operation conditions determined by the engine revolution speed andintake manifold pressure.

In the related art, Pb, that is, Pw which is the wet air pressure, hasbeen used as the intake manifold pressure in Expression (7), whichresulted in an error caused by humidity. By contrast, in the presentEmbodiment 1, the amount Qd of dry air can be calculated by using thedry air partial pressure Pd calculated with Expression (6) above. As aresult, the error caused by humidity can be eliminated.

The fuel injection amount calculation unit 105 inputs the dry airpartial pressure Pd and operation information of various types andcalculates and outputs the fuel injection amount, that is, the driveamount of the injector 10. It is a generally well-known technique tocalculate the fuel injection amount realized by the injector 10 underthe engine control on the basis of the target ratio (referred tohereinbelow as A/F) of the air mass and fuel mass in the operation stateand the intake air amount during the operation.

Accordingly, in Embodiment 1, the amount of fuel which is optimum forrealizing the target A/F can be calculated by using the amount Qd of dryair, which contributes to combustion, as the amount of air to be usedfor calculating the fuel injection amount.

A catalyst serving to purify the exhaust gas is typically installed inthe engine exhaust channel, and the combustion state with astoichiometric A/F of 14.7 is suitable for exhaust gas purification withthe catalyst. Since the A/F can be accurately realized by calculatingthe amount of fuel from the amount of dry air, the shift in the amountof fuel, that is, the A/F, which is caused by the effect of humidity,can be suppressed and the deterioration of exhaust gas can be improved.

The ignition timing calculation unit 106 inputs the amount Qd of dry airand the mole fraction χv and calculates and outputs the ignition timing,that is, the drive timing of the ignition coil 13. It is a generallywell-known technique to calculate the ignition timing for the ignitioncoil 13 and ignition plug in engine control on the basis of the enginerevolution speed and filling efficiency. The optimum ignition timing ateach engine revolution speed and filling efficiency is measured inadvance and stored as a map inside the ignition timing calculation unit106.

The optimum ignition timing, as referred to herein, is generally theignition timing retarded from both the minimum advance for the besttorque (MBT) ignition timing and the critical ignition timing at whichknocking does not occur. In Embodiment 1, the optimum ignition timing inthe operation state can be calculated by using the amount Qd of dry airwhich contributes to the combustion also for calculating the fillingefficiency to be used for ignition timing calculation.

FIG. 3 illustrates a torque curve in a certain operation state ofEmbodiment 1 of the present invention. The torque curve, as determinedherein, is a curve representing the relationship between the ignitiontiming and the torque generated by the engine when the engine revolutionspeed and throttle opening degree in the operation state of the engine,that is, the intake air amount, A/F, and in some engine systemconfigurations the operation timing of the intake valve and theoperation timing of the exhaust valve, are all constant and only theignition timing is changed.

In the curve which curves out upward, the ignition timing at which thetorque is at a maximum is referred to as the aforementioned MBT. Forexample, the torque curve C_dry represented by a solid line in the FIG.3 is calculated in a state in which the air taken in by the engine isdry at certain engine revolution speed and filling efficiency. The MBTat this time is SA_dry, and the torque generated by the engine at theMBT is Trq_dry.

The curve C_wet represented by a broken line is obtained by increasingthe air humidity and measuring the torque curve at a high-humidity airintake while the mass flow rate of the air taken into the engine remainsconstant. The MBT at this time is SA_wet, and the torque generated bythe engine at the MBT is Trq_wet.

As depicted in FIG. 3, due to increase in humidity, the output torquedecreases and the MBT advances with respect to those when the air isdry. This is because the increase in humidity decreases the amount ofdry air taken in by the engine. The torque curve C_wet measured with thehigh-humidity air has been confirmed to represent the samecharacteristic as when the throttle valve is closed to reduce the intakeair amount during the operation with the dry air.

In other words, by calculating the filling efficiency, which is used forcalculating the ignition timing, on the basis of the amount of dry air,it is possible to perform the control by the ignition timing in thecorrect engine output characteristic.

Where the ignition timing map is to be measured and set with the dryair, with the conventional control involving no correction for humidity,even when the C_wet characteristic is realized during the high-humidityoperation, the ignition timing is calculated as SA_dry. Therefore, theignition is retarded from the MBT in the engine characteristic.

As a result, a torque loss such as Trq_loss depicted in FIG. 3 occursand fuel efficiency is degraded. By contrast in Embodiment 1, theignition timing is calculated based on the filling efficiency at theamount of dry air as a result of correction for humidity. As aconsequence, the ignition at the SA_wet, which is the MBT, becomespossible, and the resultant effect is that the fuel efficiency can beimproved by comparison with that attained with the conventional control.

FIG. 4 illustrates a torque curve in a certain operation state, which isdifferent from that depicted in FIG. 3, and a knocking limit inEmbodiment 1 of the present invention. In the dry air, where theignition timing is advanced to a BLD_dry, the knocking phenomenon occursat a level that cannot be allowed where the engine performance anddurability are taken into account. Thus, the BLD_dry indicates theignition timing at the knocking limit, and the torque generated by theengine at this time is Trq_k_dry.

The knocking limit is an ignition timing retarded from the MBT, and aknocking limit value on the retard side, or a value which is furtherretarded with consideration for the spread among the engines andenvironmental conditions, is set on the ignition timing map. It has beengenerally confirmed that in the high-load operation region of theengine, the knocking limit tends to be retarded from the MBT.

Where similar measurements are performed in a high-humidity intake airstate, since the combustion rate inside the cylinder is reduced by watervapors, the ignition timing of the knocking limit changes to a BLD_wetwhich is on the advance side, and the torque generated by the engine atthis time rises to the Trq_k_wet.

In other words, with the operation in which the knocking limit, ratherthan the MBT, is set at the ignition timing map, the ignition timing canbe further advanced during the high-humidity operation. As a result ofthe ignition timing being further advanced, the fuel efficiency can beimproved.

Even when the ignition timing in a high-humidity state is calculatedusing the amount of dry air, an additional advance is made possible withthe operation state in which the knocking limit is set at the ignitiontiming map. This result indicates that the additional improvement infuel efficiency can be attained by using the humidity information tocalculate the corrected value on the advance side and correct theignition timing calculated from the map.

The correction value, that is, the advance amount, increases as thehumidity rises. Therefore, it is possible to store in advance thehumidity information, for example, the relationship between the molefraction χv and the advance amount, as a map and calculate the advanceamount by using this map. Further, with consideration for the enginecharacteristics, the knocking limit is set at the ignition timing mapfor the high-load operation state. Accordingly, the correction of theadvance amount for the humidity may be performed only in the high-loadregion.

Returning to the explanation of FIG. 2, the target throttle openingdegree calculation unit 107 takes the intake manifold pressure Pb, thatis, the wet air pressure Pw, and the mole fraction χv as inputs andcalculates and outputs the target throttle opening degree for realizingthe target intake air amount.

As for the air amount determined by the throttle 5 in the enginecontrol, the target throttle opening degree is determined, as mentionedhereinabove, for example, by calculating the target torque from theinputted data, calculating the target intake air flow rate at which thecalculated target torque is reached, and calculating the targeteffective opening area such that the target intake air flow rate isreached. The relationship between the intake air amount and effectiveopening area is represented by Expression (8) below.

Here, the intake air amount Qvth is a volume flow rate, α0 is the soundvelocity of the intake air, Sth is the effective opening area of thethrottle, κ is the specific heat ratio of the intake air, and Pup is apressure upstream of the throttle valve. In the present invention, theatmospheric pressure Pdwn is the intake manifold pressure which is thepressure downstream of the throttle valve.

$\begin{matrix}{Q_{vth} = {{\alpha 0} \times S_{th} \times \sqrt{\frac{2}{\kappa - 1} \times \left\{ {\left( \frac{P_{dwn}}{P_{up}} \right)^{\frac{2}{\kappa}} - \left( \frac{P_{dwn}}{P_{up}} \right)^{\frac{\kappa + 1}{\kappa}}} \right\}}}} & (8)\end{matrix}$

Where the Expression (8) above is rewritten as the effective openingarea Sth, Expression (9) below is obtained. Here, a is a dimensionlessflow rate changing according to a pressure ratio Pdwn/Pup. Where thepressure ratio Pdwn/Pup is equal to or less than a critical pressureratio (in the case of air, a value corresponding to about 0.528), thedimensionless flow rate σ at the time of the critical pressure ratio isa constant value represented by Expression (10) below.

$\begin{matrix}{S_{th} = \frac{Q_{vth}}{{\alpha 0} \times \sigma}} & (9) \\{\sigma = \sqrt{\frac{2}{\kappa - 1} \times \left\{ {\left( \frac{P_{dwn}}{P_{up}} \right)^{\frac{2}{\kappa}} - \left( \frac{P_{dwn}}{P_{up}} \right)^{\frac{\kappa + 1}{\kappa}}} \right\}}} & (10)\end{matrix}$

A model using a physical computational formula may be used forcalculating the opening degree of the throttle from the effectiveopening area on the basis of the throttle valve shape, or valuescalculated in advance on the basis of calculation and actual measurementresults may be stored as a map and the opening degree may be calculatedusing the map.

The target intake air amount which is calculated from the target torqueneeds to be calculated based on the dry air contributing to combustion.Meanwhile, the amount of air used for the throttle opening degreecalculation needs to be calculated by the total amount of air passingthrough the throttle, that is, the amount of wet air. The flow rate Qvthrepresented by Expression (8) above is a volume flow rate, but the ratioof the number of moles is the same as the volume ratio. Therefore, inExpression (11) below, the volume flow rate Qvw of the wet air can becalculated from the mole fraction χv and the volume flow rate Qvd of thedry air.

$\begin{matrix}{Q_{vw} = \frac{Q_{vd}}{1 - X_{v}}} & (11)\end{matrix}$

Thus, the amount of air for realizing the target torque can beaccurately calculated without affecting the humidity state of theenvironment. It is generally well known that the conversion between themass flow rate and volume flow rate of the air can be performed by usingthe density of air.

Thus, the degradation of exhaust gas can be suppressed and the engineoutput torque can be accurately controlled, while improving the fuelefficiency, by adequately switching the pressure to be used between thedry air partial pressure and wet air pressure with the control element.

The control processing sequence in Embodiment 1 will be explainedhereinbelow by using a flowchart. FIG. 5 is a flowchart illustrating theprocessing sequence in the control method for an internal combustionengine which is executed by the ECU 20 in Embodiment 1 of the presentinvention. The processing represented by the flowchart depicted in FIG.5 is repeatedly executed by a computational processing device located inthe ECU 20 for each predetermined computational period by executing thesoftware (program) stored in the storage device.

Initially, in step S501, the ECU 20 performs the processing of thesaturated water vapor pressure calculation unit 101 and the water vaporpartial pressure calculation unit 102. More specifically, the saturatedwater vapor pressure Ps is calculated from the intake temperature Tafsby the processing of the saturated water vapor pressure calculation unit101, and the water vapor partial pressure Pv is calculated from therelative humidity Hafs and the saturated water vapor pressure Ps by theprocessing of the water vapor partial pressure calculation unit 102.

Then, in step S502, the ECU 20 performs the processing of the molefraction calculation unit 103. More specifically, the mole fraction χvcorresponding to the humidity information is calculated from theatmospheric pressure Pa and the water vapor partial pressure Pv by theprocessing of the mole fraction calculation unit 103.

Then, in step S503, the ECU 20 performs the processing of the dry airpartial pressure calculation unit 104. More specifically, the dry airpartial pressure Pd is calculated from the intake manifold pressuresensor Pb and the mole fraction χv by the processing of the dry airpartial pressure calculation unit 104.

Then, in step S504, the ECU 20 performs the processing of the fuelinjection amount calculation unit 105, the ignition timing calculationunit 106, and the target throttle opening degree calculation unit 107.More specifically, the fuel injection amount is calculated from the dryair partial pressure Pd by the processing of the fuel injection amountcalculation unit 105, the ignition timing is calculated from the dry airpartial pressure Pd or the dry air partial pressure Pd and the molefraction χv by the processing of the ignition timing calculation unit106, and the target throttle opening degree is calculated from the wetair pressure Pw and the mole fraction χv by the processing of the targetthrottle opening degree calculation unit 107.

As described hereinabove, the control device for an internal combustionengine according to Embodiment 1 is configured to perform the correctionof the wet air pressure which is affected by the humidity, calculatingthe dry air partial pressure from the wet air pressure after thecorrection, and switching the pressure to be used to either one of thewet air pressure and dry air partial pressure with the element of enginecontrol.

More specifically, the pressure to be used is switched such that the dryair partial pressure is used when the fuel injection amount and ignitiontiming are calculated, and the wet air pressure is used when the targetthrottle opening degree is calculated. Thus, the humidity information isused with respect to the ignition timing, and when the humidity is high,the ignition timing is corrected to the advance side.

As a result, it is possible to realize a control device for an internalcombustion engine and a control method for an internal combustion enginethat can suppress the degradation of exhaust gas and accurately controlthe engine output, while improving the fuel efficiency.

What is claimed is:
 1. A control device for an internal combustionengine, the control device comprising: an operation state detector thatdetects an operation state of an internal combustion engine; an intakemanifold pressure detector that detects a pressure in an intake manifolddownstream of a throttle valve provided in an intake channel of theinternal combustion engine; an air humidity detector that detects ahumidity of air taken in by the internal combustion engine; an airtemperature detector that detects the temperature of the air; anatmospheric pressure detector that detects an ambient pressure of theinternal combustion engine as an atmospheric pressure; and a controllerthat controls an engine output on the basis of detection results of thedetectors, wherein the controller: generates humidity information on theair which is taken in by the internal combustion engine, from thehumidity detected by the air humidity detector, the temperature detectedby the air temperature detector, and the atmospheric pressure detectedby the atmospheric pressure detector; calculates a dry air partialpressure by correcting the pressure detected by the intake manifoldpressure detector, by using the generated humidity information; andcontrols the engine output by taking the pressure detected by the intakemanifold pressure detector as a wet air pressure and selecting,according to a control element, either one of the wet air pressure andthe dry air partial pressure as a pressure to be used for controllingthe engine output.
 2. The control device for an internal combustionengine according to claim 1, wherein the air humidity detector detectsthe humidity as a relative humidity, and the controller calculates amole fraction represented by a ratio of the atmospheric pressure and awater vapor partial pressure on the basis of the relative moisture, andtakes the calculated mole fraction as the humidity information.
 3. Thecontrol device for an internal combustion engine according to claim 1,wherein when the control element is a fuel injection amount, thecontroller calculates the fuel injection amount by using the dry airpartial pressure.
 4. The control device for an internal combustionengine according to claim 2, wherein when the control element is a fuelinjection amount, the controller calculates the fuel injection amount byusing the dry air partial pressure.
 5. The control device for aninternal combustion engine according to claim 1, wherein when thecontrol element is an ignition timing, the controller calculates theignition timing by using the dry air partial pressure.
 6. The controldevice for an internal combustion engine according to claim 2, whereinwhen the control element is an ignition timing, the controllercalculates the ignition timing by using the dry air partial pressure. 7.The control device for an internal combustion engine according to claim3, wherein when the control element is an ignition timing, thecontroller calculates the ignition timing by using the dry air partialpressure.
 8. The control device for an internal combustion engineaccording to claim 5, wherein when the humidity information is higherthan a predetermined threshold, the controller corrects the ignitiontiming to an advance side.
 9. The control device for an internalcombustion engine according to claim 6, wherein when the humidityinformation is higher than a predetermined threshold, the controllercorrects the ignition timing to an advance side.
 10. The control devicefor an internal combustion engine according to claim 7, wherein when thehumidity information is higher than a predetermined threshold, thecontroller corrects the ignition timing to an advance side.
 11. Thecontrol device for an internal combustion engine according to claim 1,wherein when the control element is a target throttle opening degree ofan electronically controlled throttle, the opening degree of which canbe electrically adjusted to adjust an intake air amount, the controllercorrects, by using the humidity information, a target intake air amountfor realizing a request torque of the internal combustion engine andcalculates the target throttle opening degree by using the target intakeair amount corrected by the humidity information and the wet airpressure.
 12. The control device for an internal combustion engineaccording to claim 2, wherein when the control element is a targetthrottle opening degree of an electronically controlled throttle, theopening degree of which can be electrically adjusted to adjust an intakeair amount, the controller corrects, by using the humidity information,a target intake air amount for realizing a request torque of theinternal combustion engine and calculates the target throttle openingdegree by using the target intake air amount corrected by the humidityinformation and the wet air pressure.
 13. The control device for aninternal combustion engine according to claim 3, wherein when thecontrol element is a target throttle opening degree of an electronicallycontrolled throttle, the opening degree of which can be electricallyadjusted to adjust an intake air amount, the controller corrects, byusing the humidity information, a target intake air amount for realizinga request torque of the internal combustion engine and calculates thetarget throttle opening degree by using the target intake air amountcorrected by the humidity information and the wet air pressure.
 14. Thecontrol device for an internal combustion engine according to claim 4,wherein when the control element is a target throttle opening degree ofan electronically controlled throttle, the opening degree of which canbe electrically adjusted to adjust an intake air amount, the controllercorrects, by using the humidity information, a target intake air amountfor realizing a request torque of the internal combustion engine andcalculates the target throttle opening degree by using the target intakeair amount corrected by the humidity information and the wet airpressure.
 15. The control device for an internal combustion engineaccording to claim 15, wherein when the control element is a targetthrottle opening degree of an electronically controlled throttle, theopening degree of which can be electrically adjusted to adjust an intakeair amount, the controller corrects, by using the humidity information,a target intake air amount for realizing a request torque of theinternal combustion engine and calculates the target throttle openingdegree by using the target intake air amount corrected by the humidityinformation and the wet air pressure.
 16. The control device for aninternal combustion engine according to claim 6, wherein when thecontrol element is a target throttle opening degree of an electronicallycontrolled throttle, the opening degree of which can be electricallyadjusted to adjust an intake air amount, the controller corrects, byusing the humidity information, a target intake air amount for realizinga request torque of the internal combustion engine and calculates thetarget throttle opening degree by using the target intake air amountcorrected by the humidity information and the wet air pressure.
 17. Thecontrol device for an internal combustion engine according to claim 7,wherein when the control element is a target throttle opening degree ofan electronically controlled throttle, the opening degree of which canbe electrically adjusted to adjust an intake air amount, the controllercorrects, by using the humidity information, a target intake air amountfor realizing a request torque of the internal combustion engine andcalculates the target throttle opening degree by using the target intakeair amount corrected by the humidity information and the wet airpressure.
 18. A control method for an internal combustion engine whichis executed by a controller in a control device for an internalcombustion engine, the control device including: an operation statedetector that detects an operation state of an internal combustionengine; an intake manifold pressure detector that detects a pressure inan intake manifold downstream of a throttle valve provided in an intakechannel of the internal combustion engine; an air humidity detector thatdetects a humidity of air taken in by the internal combustion engine; anair temperature detector that detects the temperature of the air; anatmospheric pressure detector that detects an ambient pressure of theinternal combustion engine as an atmospheric pressure; and thecontroller that controls an engine output on the basis of detectionresults of the detectors, the control method comprising the followingsteps executed by the controller: a first step for generating humidityinformation on the air which is taken in by the internal combustionengine, from the humidity detected by the air humidity detector, thetemperature detected by the air temperature detector, and theatmospheric pressure detected by the atmospheric pressure detector; asecond step for calculating a dry air partial pressure by correcting thepressure detected by the intake manifold pressure detector by using thehumidity information generated in the first step; and a third step forcontrolling the engine output by taking the pressure detected by theintake manifold pressure detector as a wet air pressure and selecting,according to a control element, either one of the wet air pressure andthe dry air partial pressure as a pressure to be used for controllingthe engine output.